Conditions in a producing fluid well such as an oil or gas well often require the introduction of treatment chemicals. For example, inhibitors to prevent corrosion scale build-up, waxing or other undesirable conditions are commonly introduced as required in a variety of ways. Chemicals in liquid form have been introduced by being pumped or poured down the tubing string or the production string, and have also been injected through separate strings of tubing. All of these methods, however, suffer from major disadvantages. The use of additional strings of tubing is costly and can interfere with other operations, while the use of liquid chemicals can require great quantities in order to ensure adequate distribution throughout the well, at an excessively high cost.
Treatment compositions have also been introduced from containers which are designed to release the composition after reaching the point in the well where it is desired to have the treatment begin. One approach has been to utilize a carrier which is dissolved by the treatment composition itself, an example of which is disclosed in U.S. Pat. No. 4,611,664 to Osterhoudt, III et al. In this arrangement the well is taken off production and the carrier, which is designed to disintegrate shortly after it reaches the bottom of the well, is dropped into the well. After a period of time the well is returned to production. The resulting flow of well fluid causes the liquid chemical composition to mix with the well fluid. This method of treatment does not lend itself to wells containing fluid which is highly corrosive or which precipitates scale at a rapid rate because the treatment would have to be carried out so often that it would be impractical to take the well off production each time. Further, the concentration of treatment liquids is difficult to control since the manner of introduction in effect is a batch treatment process.
The use of solid treatment material in the form of shaped rods has been suggested, but this approach also suffers from problems similar to those discussed above. Well production normally is interrupted during the period of treatment, which preferably should be avoided if practicable. Further, the rapid disintegration of the rods results in a batch process type of treatment, with consequent difficulties in accurately controlling the treatment operation.
It has also been suggested to provide a container which would release treatment composition over a longer span of time. Such an arrangement is disclosed in U.S. Pat. No. 2,775,302 to Kirkpatrick, wherein a carrier separated into several compartments is disclosed. By making the walls separating the compartments of varying thickness the well fluid is caused to corrode through the thinner walls first, thereby releasing the chemicals in the compartment bounded by those walls. The chemicals in the other compartments are subsequently released when their thicker walls are corroded away. In this manner the treatment period is extended over a period of days. Although the treatment extends over a greater period of time than the previously described processes, it is still basically a batch treatment process, since all of the chemicals within a particular compartment are released at the same time. It is merely the interval between releases that is controlled. Such an arrangement does not provide for the steady introduction of controlled amounts of chemicals suitable for use in a well which contains highly corrosive well fluid and which therefore requires greater overall quantities of treatment composition to be introduced.
Still another way of introducing treatment composition is disclosed in U.S. Pat. No. 2,635,996 to Rohrback et al. In that patent a metal shell one to four feet in length is filled with a treatment composition, and the open end is either narrowed by pinching it together until only a narrow space remains or is sealed with a high melting point wax. The treatment composition is a solid and is dissolved by the well fluid at the top of the metal shell until the shell disintegrates in about 24 hours. Thus even though the composition is released into the well over a period of time, the release period itself is so short as to simply constitute another variation of a batch-type chemical introduction process.
Instead of the short term introduction methods of the prior art, with their resulting problems of cost and control, it would be highly desirable to develop a well treatment method which is operative over a long period of time and which can be designed to introduce compositions into a well at predetermined rates. It would also be desirable to do this without having to interrupt well production over this period of time.